Dual threshold overcurrent reset

Abstract

A method of operating a power conversion system including converting variable frequency AC voltage to constant frequency AC voltage by a power converter, setting a first peak current reset threshold above operating currents previously observed during steady state short circuit current regulation in by a controller of the power converter, setting a second peak current reset threshold at a current lower than the previously observed steady state short-circuit regulation point observed during previous operation during steady state short circuit current regulation by the controllers of the power converter, resetting inverter converter AC output regulating voltage to 0 volts, and ramping AC output regulating voltage back up into steady-state operation when the second a peak current reset threshold is exceeded.

What is claimed is: 
     
       1. A method of operating a power conversion system comprising the steps of:
 converting variable frequency AC voltage to constant frequency AC voltage by a power converter; 
 setting a first peak current reset threshold above operating currents previously observed during steady state short circuit current regulation by a controller of the power converter; 
 setting a second peak current reset threshold at a current lower than the previously observed steady state short-circuit regulation point during steady state short circuit current regulation by the controllers of the power converter; 
 resetting converter AC output regulating voltage to 0 volts; and 
 ramping AC output regulating voltage back up into steady-state operation when the second peak current reset threshold is exceeded; 
 wherein if a short circuit is present, the AC output regulating voltage and current output ramp up at a controlled rate; and 
 increasing an inverter operating duty cycle up to a value where a controller is limiting and regulating short circuit currents. 
 
     
     
       2. The method of  claim 1 , further comprising raising the second peak current reset threshold to the first peak current reset threshold in order to allow for the converter to deliver short circuit currents levels. 
     
     
       3. The method of  claim 1 , wherein the inverter operating duty cycle is increased to a preset short circuit rms current reference value of 1.5 to 2.5 times rated load current. 
     
     
       4. The method of  claim 1 , wherein if the AC output voltage is overloaded but no short circuit is present, the AC output voltage ramps up to a value set by a pre-determined fold-back curve. 
     
     
       5. The method of  claim 4 , wherein the foldback curve, represents a relationship between output voltage and load current produced by a variable speed constant frequency (VSCF). 
     
     
       6. The method of  claim 4 , wherein when the power converter has ramped up to the value determined by the pre-determined fold-back curve or short-circuit current reference value, a higher reset detection threshold is set by the controller to be used for any subsequent resets of the output voltage.